Plants growth and development is depends on light energy of the sun. This energy thru photosynthesis is using for production of carbohydrates and other photo-assimilates. Part of produced carbohydrates is consuming by the same tissues for growth and development, while excess materials are trans -locates to other consumer or storage organs. Accordingly, plants parts are classified in source and sink organs. In order to improve crop yield by using relevant knowledge, this detailed review aimed to provide valuable information about biochemical and molecular mechanisms of production and consumption of photo-assimilates in different plant organs for breeding proposes. Source and sink strength like many other biological processes, are related to plant genetic potential, rate and type of plant response to environmental condition, efficiency of biochemical mechanisms and ability of involved enzymes in production and transporting photo-assimilates. This paper is intended to evaluate the recent advances in source and sink specifications, particularly in wheat. It has been attempted to identify indigenous attributes related to source and sink strength, determination of soluble carbohydrate production circumstances along with activity of involved key enzymes at different tissues, which might be suitable for increased plant performance, particularly in stressful environments like drought stress